The present invention relates to an internal combustion engine capable of switching between spark ignition combustion and compression ignition combustion, and in particular relates to control for such an internal combustion engine after fuel-cut.
A compression ignition type of internal combustion engine has advantage that fuel efficiency is high because high compression ratio is achieved. Such an engine has further advantage that the amount of NOx emission is low because the combustion temperature is low.
In order to cause the compression self-ignition, the temperature of gas within a combustion chamber needs to be raised beyond a predetermined temperature. Heating of intake air or internal EGR is typically performed so as to raise the temperature within the combustion chamber.
The temperature within the combustion chamber may not reach the predetermined temperature, for example, when the engine load is low. If the temperature within the combustion chamber is lower than the predetermined temperature, engine misfire may occur even when the piston reaches the top dead center (TDC). In order to prevent such engine misfire, the engine combustion is switched to spark ignition when the temperature within the combustion chamber is low, as described in the Japanese Patent Application Unexamined Publication (Kokai) No. 2000-87749.
Fuel cut, which temporarily cuts fuel supply to the engine, may be performed in response to deceleration of the vehicle. Such fuel cut decreases the temperature within the combustion chamber and the temperature of exhaust gas used for internal EGR. If the engine combustion is switched to compression ignition after the fuel-cut, the temperature within the combustion chamber may not reach a temperature required for the compression self-ignition. Even if operating conditions of the engine are within a range where the compression ignition combustion is allowed, engine misfire may occur because the temperature within the combustion chamber is low.
Thus, there is a need for technique that prohibits the compression ignition combustion if the temperature within the combustion chamber immediately after fuel-cut does not reach a predetermined value that is required for the compression self-ignition.